Table of Contents
- Introduction
- Understanding the Dahlia Lifecycle
- Timing Your Harvest
- Step 1: Cutting Back the Foliage
- Step 2: Digging with Care
- Step 3: Cleaning and Curing
- Step 4: The Debate: Fall vs. Spring Dividing
- Step 5: Identifying and Labeling
- Step 6: Packing Methods for Winter
- Step 7: Finding the Ideal Storage Spot
- Winter Maintenance: The Monthly Check-In
- Preparing for Spring
- Conclusion
- FAQ
Introduction
Dahlias are the undisputed stars of the late-summer garden. From the massive, billowy petals of dinnerplate varieties like 'Cafe au Lait' to the perfectly symmetrical shapes of ball dahlias, these plants provide a wealth of color when other flowers begin to fade. Because they are native to the warm climates of Mexico and Central America, they treat our summer sun like a long vacation. However, as the seasons shift and the first frost approaches, these tropical beauties need a little help to survive the cold months.
At Longfield Gardens, we believe that saving your dahlia tubers is one of the most rewarding parts of the gardening cycle. It allows you to grow your collection year after year and even share your favorite varieties with friends. Storing tubers might seem like a complex task reserved for experts, but it is actually quite simple once you understand the basic needs of the plant.
This guide will walk you through the entire process, from the first frost to the final winter check-in. We will cover the best tools for the job, how to cure your tubers for long-term health, and the ideal storage conditions to ensure they wake up ready to bloom next spring. With a few easy steps, you can keep your garden’s most spectacular performers safe and sound all winter long.
Understanding the Dahlia Lifecycle
To store dahlias successfully, it helps to understand what the plant is doing as autumn arrives. In their native environment, dahlias do not have to deal with freezing ground. In the United States, most gardeners live in zones where the soil temperature drops low enough to damage or kill the fleshy tubers.
As the days get shorter and the air turns crisp, the dahlia plant begins to move its energy from the leaves and flowers down into the root system. These roots, or tubers, act like a pantry. They store all the starches and nutrients the plant needs to sprout again when warm weather returns. By digging them up and storing them in a protected space, you are simply giving them a safe place to take a "winter nap."
Timing Your Harvest
One of the most important rules for dahlia storage is to let nature tell you when it is time to start. While it might be tempting to dig them up as soon as the flowers stop blooming, waiting for the right moment ensures the tubers are mature and hardy.
The Signal of the First Frost
The best time to dig your dahlias is usually right after the first killing frost. You will know this has happened when the lush green foliage turns black or dark brown overnight. This sight might look a bit sad at first, but it is a natural part of the process. This frost tells the plant to go dormant, which is a deep state of rest.
If you live in a region where a hard frost does not arrive until very late in the year, you can still dig your tubers in late October or early November. The goal is to get them out of the ground before the soil itself freezes solid. A light frost that only nips the top leaves is fine, but a "killing frost" that turns the whole plant dark is the perfect green light to begin.
The Benefits of Waiting
If your schedule allows, wait about five to seven days after the foliage turns black before you dig. During this week, the tubers undergo a final "curing" process while still in the ground. They develop a slightly thicker skin and the "eyes"—the small bumps where next year's stems will grow—often become more visible. This short wait makes the tubers more resilient during their months in storage.
What to do next:
- Monitor your local weather forecast for the first frost.
- Prepare your tools: a garden fork, sharp loppers, and labeling materials.
- Clear a space in a garage or basement for the initial drying phase.
Step 1: Cutting Back the Foliage
Once the plants have been hit by frost and you are ready to dig, the first practical step is to clear away the top growth. The thick, hollow stems of a dahlia can be quite large by the end of summer, especially for tall decorative varieties.
Use a pair of sharp loppers or heavy-duty garden shears to cut the stems down. Leave about four to six inches of the main stem protruding from the ground. This remaining piece of stem acts as a "handle" that helps you lift and move the clump without putting stress on the fragile tubers themselves.
Avoid cutting the stems all the way to the soil level. The crown, which is the area where the tubers meet the stem, is where the growth eyes are located. Keeping a bit of the stem intact helps protect this vital area from damage during the digging process.
Step 2: Digging with Care
Dahlia tubers are surprisingly heavy, but they are also quite brittle. The neck of the tuber—the thin part that connects the fleshy body to the central stalk—is easily snapped. If the neck breaks, the tuber usually cannot grow a new plant, even if the rest of the root looks healthy.
Using the Right Tools
A garden fork (sometimes called a pitchfork) is generally better than a shovel for this job. Shovels have a solid blade that can easily slice through a hidden tuber. The tines of a garden fork allow you to loosen the soil and lift the clump with much less risk of accidental damage.
The Lifting Technique
Start by inserting your fork into the ground about 12 inches away from the main stem. You want to give the clump plenty of room, as some varieties produce tubers that spread out wide. Gently pry the fork upward to loosen the soil, then move to the opposite side and repeat the process.
Work your way around the plant in a circle, loosening the earth as you go. Once the soil is soft and the clump feels loose, use the "handle" of the stem and the fork together to lift the tubers out of the ground.
Step 3: Cleaning and Curing
After the tubers are out of the ground, they need to be cleaned and "cured" before they go into their final storage containers. Curing is a fancy word for letting the outer skin dry and toughen up, which prevents rot.
To Wash or Not to Wash?
There are two main schools of thought regarding cleaning. Some gardeners prefer to wash their tubers thoroughly with a garden hose to remove all soil. This makes it much easier to see the eyes and check for any signs of damage or pests.
Other gardeners prefer to simply shake off the excess dirt and let the tubers dry with a bit of soil still clinging to them. This can act as a natural protective layer. We find that washing is often the best choice for beginners because it allows for a better inspection of the tuber's health. If you choose to wash them, do so gently. A high-pressure stream of water can sometimes peel the delicate skin.
The Initial Drying Phase
Once the tubers are clean, find a cool, dry spot away from direct sunlight and wind. A garage, a shed, or a covered porch works well. Lay the clumps out on a piece of cardboard or a mesh screen.
Turn the clumps upside down so that any water trapped in the hollow stems can drain out. If water stays inside the stem, it can lead to crown rot, which can ruin the entire clump. Let them sit in this protected spot for one to three days. You want the surface to feel dry to the touch, but you don't want the tubers to start shriveling.
Step 4: The Debate: Fall vs. Spring Dividing
One of the most common questions we hear is whether you should divide your dahlia clumps in the fall or wait until the spring. Both methods have advantages, and the right choice depends on your comfort level.
Dividing in the Fall
Dividing in the fall means you cut the large clump into individual tubers before you store them. The main benefit here is that it takes up much less space. Ten large clumps might fill several bulky bins, while the same tubers divided might fit into a few small boxes. Additionally, the stems are softer and easier to cut in the autumn.
The challenge with fall division is that the "eyes" can be very difficult to see. Each individual tuber must have a piece of the crown and at least one eye to grow. If you cut a tuber off without an eye, it will stay firm but will never produce a sprout.
Waiting Until Spring
Many home gardeners choose to store the clumps whole and divide them in the spring. During the winter, the tubers will naturally develop and the eyes will begin to swell as they "wake up" in the spring. This makes it incredibly easy to see exactly where to make your cuts. Storing the clumps whole also provides a bit more protection against drying out.
Key Takeaway: If you have plenty of storage space, keeping the clumps whole is the safest way to ensure you have viable eyes in the spring. If space is tight, dividing in the fall is a great way to stay organized.
Step 5: Identifying and Labeling
Nothing is more frustrating than a box of mystery tubers in the spring. Even if you think you will remember which clump was the tall purple one and which was the short yellow one, names and colors are easily forgotten over several months.
As soon as the tubers are dry, label them. You can use a soft pencil or a permanent marker to write the variety name directly on the skin of the tuber. It sounds simple, but it is the most effective way to keep your garden organized. If the skin is too dark or rough, you can also use flagging tape or paper tags tied loosely around the stem "handle."
Step 6: Packing Methods for Winter
Once your tubers are clean, dry, and labeled, it is time to pack them away. The goal of storage is to keep the tubers in a "Goldilocks" state: not so damp that they rot, and not so dry that they shrivel up into raisins.
Choosing Your Storage Medium
You should never store dahlia tubers in an airtight plastic bag or a sealed container. They are living things that need a tiny bit of air to breathe. Instead, use a breathable container like a cardboard box, a plastic bin with the lid left slightly ajar, or a wooden crate.
To maintain the right moisture level, you will need to pack the tubers in a "storage medium." This material surrounds the tubers and acts as a buffer against changes in humidity. Popular choices include:
- Coarse Vermiculite: This is many gardeners' favorite choice because it is sterile and does an excellent job of regulating moisture.
- Pine Shavings: Often sold as pet bedding, these are inexpensive and provide great airflow.
- Peat Moss: A classic choice, though it can be dusty to work with.
- Wood Chips: Similar to shavings, these work well in slightly damp basements.
The Layering Technique
Place a two-inch layer of your chosen medium at the bottom of your container. Arrange your tubers or clumps on top so they are not touching each other. If one tuber happens to rot, keeping them separate prevents the rot from spreading to the rest of the group. Cover them with more medium and repeat the layers until the box is full.
Step 7: Finding the Ideal Storage Spot
The location where you keep your boxes is just as important as how you pack them. In our trial gardens at Longfield Gardens, we have found that temperature is the deciding factor in storage success.
The "Sweet Spot" for Temperature
The ideal temperature for dahlia storage is between 40°F and 50°F. If the temperature stays in this range, the tubers will remain dormant and happy.
- If it gets too cold: If the temperature drops below freezing (32°F), the water inside the tubers will freeze, causing the cells to burst. When they thaw, the tubers will turn into a soft, black mush.
- If it gets too warm: If the temperature stays above 55°F, the tubers may think it is spring and start to sprout prematurely, or they may simply dry out too quickly.
Common Storage Locations
A cool basement, a crawl space, or an unheated (but attached) garage are usually the best spots. Avoid spots near a furnace or water heater, as these areas are often too dry and warm. If you are using a garage, make sure the boxes are elevated off the concrete floor, which can pull cold and moisture into the containers.
Winter Maintenance: The Monthly Check-In
Storing dahlia tubers is not a "set it and forget it" task. To ensure the highest success rate, you should check on your tubers about once a month throughout the winter. This allows you to catch small issues before they become big problems.
Checking for Rot
If you see a tuber that has become soft, slimy, or smells unpleasant, it is starting to rot. Remove it immediately and throw it away. If the rot is only on a small part of a large clump, you can sometimes cut away the damaged area with a clean knife and let the healthy part continue to store.
Checking for Shriveling
If the tubers are looking wrinkled or feel lightweight, they are losing too much moisture. This is a common issue in modern basements that have very low humidity. If this happens, use a spray bottle to lightly mist the storage medium with water. You don't want it to be wet—just a tiny bit of dampness is enough to stop the shriveling.
Winter Checklist:
- Open the boxes once a month to check for airflow.
- Feel the tubers for firmness.
- Remove any "bad apples" that show signs of decay.
- Lightly mist the packing material if it feels bone-dry.
Preparing for Spring
As the days begin to lengthen in late March or April, you can start thinking about the upcoming season. This is the time to bring your boxes out of their cold storage spots and into a slightly warmer area.
If you stored your clumps whole, you will likely see the eyes beginning to swell and turn pink or green. This is the perfect time to divide them, as the growth points are now obvious. You can even "pre-start" your dahlias indoors in pots about four to six weeks before the last frost date. This gives them a head start and leads to earlier blooms in the summer.
We ship our dahlia tubers in the spring according to your USDA hardiness zone, so they arrive right when it is the ideal time to plant or start them indoors. Seeing those first green sprouts emerge from a tuber you saved yourself is a wonderful feeling that makes the winter wait worthwhile.
Conclusion
Storing dahlia tubers over winter is a simple, effective way to enjoy your favorite flowers year after year. By following the natural cycle of the plant—waiting for the frost, curing the roots, and providing a cool, stable environment—you can protect your investment and even grow your garden for free. While the process requires a bit of patience, the reward is a summer landscape filled with spectacular blooms that feel like old friends.
- Wait for the first killing frost before digging to ensure tuber maturity.
- Cure the tubers in a cool, dry place for a few days to toughen the skin.
- Store in a breathable medium like vermiculite at 40-50°F.
- Check monthly for rot or shriveling to keep your stock healthy.
Successfully overwintering your dahlias turns a seasonal hobby into a lifelong passion. The team at Longfield Gardens is always here to help you grow a more beautiful garden, one season at a time.
FAQ
Can I store dahlia tubers in my refrigerator?
While a refrigerator stays in the correct temperature range, it is usually too dry for long-term dahlia storage. Additionally, many refrigerators contain fruits like apples that release ethylene gas, which can damage the tubers. It is better to use a cool basement or an unheated closet where the humidity is more stable.
What should I do if my tubers look moldy during the winter?
A small amount of surface mold is usually not a cause for panic. It often means the storage medium is a bit too damp or there isn't enough airflow. Gently wipe the mold off with a dry cloth and leave the lid of your storage bin open for a few days to let the excess moisture evaporate. If the tuber is soft or mushy, however, it should be discarded.
Do I have to wash the tubers before storing them?
You do not have to wash them, and some gardeners prefer the "dry brush" method where they simply knock off the big clumps of soil. However, washing makes it much easier to see the growth eyes and any hidden rot. If you grow in heavy clay soil, washing is highly recommended as clay can trap too much moisture against the skin during storage.
How do I know if a dahlia tuber is "dead" in the spring?
A healthy tuber should feel firm, similar to a potato. If a tuber is completely hollow, papery, or shriveled to the point of being brittle, it is likely dead and won't grow. Most importantly, look for the "eye" near the stem. If there is a small bump or a green sprout, the tuber is alive and ready to be planted.